Type I GaSb1-xBix/GaSb quantum wells dedicated for mid infrared laser applications: Photoreflectance studies of bandgap alignment

Abstract

To determine the band alignment at the GaSb 1-x Bi x /GaSb interface, a set of GaSb 1-x Bi x /GaSb quantum wells (QWs) of various widths (7, 11, and 15 nm) and contents (Bi ≤ 12%) were grown by molecular beam epitaxy and investigated by photoreflectance (PR) spectroscopy. In PR spectra, the optical transitions related to both the ground and the excited states in the QW were clearly observed. It is a direct experimental evidence that the GaSb 1-x Bi x /GaSb QW is a type-I QW with a deep quantum confinement in both the conduction and valence bands. From the comparison of PR data with calculations of energies of QW transitions performed for the varying valence band offset (VBO), the best agreement between experimental data and theoretical calculations has been found for the VBO ∼50 ± 5%. A very similar VBO was obtained from ab initio calculations. These calculations show that the incorporation of Bi atoms into a GaSb host modifies both the conduction and valence band: the conduction-band position changes linearly at a rate of ∼15-16 meV per % Bi and the valence band position changes at a rate of ∼15-16 meV per % Bi. The calculated shifts of valence and conduction bands give the variation of VBO between GaSb 1-x Bi x and GaSb in the range of ∼48%-52%, which is in good agreement with conclusions derived from PR measurements. In addition, it has been found that the electron effective mass reduces linearly with the increase in Bi concentration (x): m GaSbBi eff ¼ m GaSb eff À 0:2x, where m GaSb eff is the electron effective mass of GaSb. Moreover, a strong photoluminescence (PL) was observed and a negligible Stokes shift (less than a few meV) between the PL peak and the fundamental transition in the PR spectrum was detected for all QWs at low temperatures. It means that the investigated QWs are very homogeneous, and the carrier localization for this alloy is very weak in contrast to other dilute bismides.

Experimental and Theoretical Studies of the Electronic Band Structure of Bulk and Atomically Thin Mo1–xWxSe2 Alloys

“…Moreover, the mentioned PR signal assignment to transitions between bands was performed, taking into account their spin-layer polarization. ,, To determine the theoretical parameters, we have calculated the electronic band structure of the Mo 1– x W x Se 2 alloy, with different W contents, as described in the Computational Methods section. The used here D3 vdW correction that is relevant for layered crystals, together with the mBJ-TB09 potential, has been shown to work successfully for TMDs. ,,, Furthermore, to reproduce the random distribution of cation (metal) atoms on crystal sites, we used the SQS approach as it was effectively applied to study semiconductor alloys. ,,− The calculated electronic band structures of MoSe 2 and WSe 2 are presented on the top panel of Figure . We consider here primarily the lowest/highest energetically located conduction/valence bands labeled by c / v letters.…”

Optical properties and dynamics of excitons in Ga(Sb, Bi)/GaSb quantum wells: evidence for a regular alloy behavior

“…The type-I Ga(Sb, Bi)/GaSb quantum well (QW) [1] is an interesting solution for fabricating optoelectronic devices operating in the ∼2-5 μm spectra range important for environmental [2,3] and medical diagnostics [4,5], free-space communication [6], and spectroscopy [7]. Incorporation of a few percents of Bi into the GaSb host (∼725 meV bandgap at T=300 K) [8] leads to a substantial bandgap reduction (30)(31)(32)(33)(34)(35) meV/at% Bi) [9][10][11] and allows to close the bandgap for III-V semiconductors.…”